Luminaire for multiple fluorescent lamps



April 29, 1941.

L c. DOANE LUMINAIRE FOR MULTIPLE FLUORESCENT LAMPS Filed March 12, 1941 LEROY C. Dams/ 5.

Patented Apr. 29, 1941 LUMINAIRE FOR MULTIPLE FLUORESCENT LAMPS Conn., assignor to The Meriden, Conn.,

Leroy C. Doane, Meriden,

Doane Products Corporation,

a corporation of Connecticut Application March- 12, 1941, Serial No. 383,033

4 Claims. (01. 240-78) The present invention relates to luminaires for multiple elongated light sources, and is more particularly directed toward such luminaires wherein a plurality of linear fluorescent lamps are in a single reflector.

Heretofore the accepted practice has been to use individual reflectors or to mount a number of these lamps laterally of the axis of the reflector. This has introduced difliculties in the design of lighting equipment for use with fluoreswave lengths that are in the visible spectrum. cent lamps, due to certain inherent character- Tubular fluorescent lamps while being more istics of the lamps, which will be detailed later eflicient than incandescent filament lamps can herein. only be made in low powered sizes to operate on The present invention contemplates a radical normal 110 volt circuits. The generation of change in the design of multiple tubular lamp light per foot of tube length is so low that a large luminaires wherein the lamps are mounted one group of fluorescent lamps must be used to equal above the other generally in the axial plane of the light generated by a single 300 or 500 watt the reflector. This method of design will overfilament lamp. Desirable levels of illumination come the difliculties heretofore encountered. are such that in all cases (except for local light- The invention also contemplates the use of ing with lamps very close to the work), it is pairs of the lamps with a minimum of space necessary to install a number of fluorescent and wiring expense, and a maximum blending of lamps in a single fixture. Due to the physical light to reduce flicker. dimensions of the lamps and low light output per A further object of the invention is to provide unit length, this means excessively large and luminaires with multiple fluorescent lamps of a expensive fixtures when the conventional methspecial cross section contour whereby the shadod of mounting multiple lamps in reflectors is owing of one lamp by another is reduced. used.

This applicationis a continuation in part of Another characteristic of fluorescent lamps applicants co-pending application for Letters operated on alternating current is that they Patent, entitled Luminaires for multiplev fluores- :m fflicker due to a change in light output during cent lamps, filed November 21', 1939,. Serial No. each alternation of current, causing a strobo- 305,439, scopic efiect where one lamp only is used. It

The accompanying drawing shows illustrative can be practically eliminated by operating one examples of multiples lamp luminaires, in aclamp on a laggin power factor. and one on a cordance with the present invention. l5 l adin p w r factor, s t one of the a p In the drawing:' will be, at its maximum brightness when the Figure 1 is a cross-section of an improved other is at a lesser brightness. Such units must two light reflector with the lamps mounted in the be lar e en u h t a da two amp axial plane of the reflector and embodied in a H wev r, alt na i cu rent tubular fluor-' fixture; 40 escent lamps require a choke, or ballast coil for,

Figure 2 is a view through the reflector and ch lamp to control the arc current. This the lamps only of the fixture of Figure 1, illuscreates a lagging power factor in the electrical trating the light control of the upper lamp on circuit that is objectionable in several ways. the left of the figure andthe light control from The la in power factor may be corrected by t lower'lamp on t right of th figure; the use of a capacity or condenser connected Figure 3 is a view similar to Figure 2, showing the light control in a Figure 4 is a graph illustrating the co-operation between lamps and reflector to efl'ect the desired mixing and distribution-of the light radiated from the lamps.

To a better understanding of the'instant invention and its accomplishments in advancing the art of illumination, it is first pointed out that unit employing lamps Of different cross-section; and

lamp is one for arc produces a radiation of ultraviolet light.

The inside of the tube is coated with appropriate phosphors that fluoresce under action of ultra ,1; violet light and re-radiate this light in longer with the choke coil to produce a leading power factor. By using lamps, half with lagging power factor and half with leading power factor, a unity power factor is obtained, and noticeable flicker is practically eliminated in the blended output of the lamps.

Fluorescent lamps have a tendency to blacken in certain areas of the tube during life. Also there are slight variations in the color 0f the light from supposedly similar lamps. By opersource. 'It consistsfof an electrode sealedin each takes place through mercury vapor within the tube and the resultant stantially uniform in 2 ating lamps in pairs in close proximity and with an immediate blending of light, it is possible to reduce the visible efiects of these variables to a minimum. This is one of the results contemplated by this invention.

Fluorescent lamps are available that will produce different colors of light. By the proper combination of lamps of two different color outputs, many additional colors may be obtained. To accomplish this successfully and to obtain an immediate balanced blend of the two colors without an unbalanced color appearance in the lighting fixture is contemplated by this invention.

In a great many commercial installations, it is desired to have a control of the intensity of lighting for difierent occasions. By means of the present invention, it is possible to construct lighting fixtures that will have a uniform lighted appearance with either all-of the lamps lighted,

or one-half of the lamps lighted.

Now, referring to the drawing, Figures 1 and 2 show the novel application of multiple linear fluorescent lamps in a single, practically parabolic, reflector, according to the present invention. The reflector 2| is, however, preferably of elongated, inverted trough-like form and in transverse vertical section defines a diverging open conic curve having a focus. In manufacturing the reflector from sheet metal it is often foundadvantageous to obtain an approximate curve by a series of breaks instead of a continuous curve. The reflector 2|, for purposes of illustration, is shown as being received in an enclosure 22 and provided with a diffusing cover 23.

Here, the lamps (two in number being shown by way of example) 24 and 25 are arranged one above and parallel to the other and lengthwise within the reflector 2| in the plane of its axis. The upper lamp 24 is positioned above the focal line and near the vertex of the reflector 2| and the lower lamp 25 below the focal line and above the plane of the open bottom or mouth of the reflector 2|, the two lamps being disposed in substantially contacting relation, with the line of such contact substantially coincident with the focal line of the reflector.

In this arrangement, and as is particularly shown in Figure 4, the opaque light reflecting surface of each lamp 24 and 25 intercepts light radiated by the other throughout a substantial angle about the axis thereof and reflects the light towards the sides of the reflector 2|, the light rays from the upper lamp 24 being projected by the reflector in an initially convergent and subsequent divergent beam 0 and the light rays from the lower lamp 25 in a wholly divergent beam d, so that the light outputs of the two lamps are mixed and combined into a substantially concentrated light flux that is subboth intensity and color- The light beams c and d, projected by the reflector 2|, have substantially the same area of coverage and the mixing of the light rays, which is efiected by the mutual reflective powers of the surfaces of the lamps and reflector, produces a projected field of soft light that is substantially free from glare and other eye-straining efiects.

By employing the second or lower lamp 25, the efiective light output of the complete fixture is practically doubled, so that the same overall efllciency of the unit is substantially maintained. At the left of Figure 2, the zone of light from the upper lamp 24 absorbed by the reflector 2| ing.

is indicated by the double diagonal cross hatching at 26, the zone of reflected light by the vertical lines at 21, the zone of direct light beyond the forty-five degree zone by horizontal lines at 28, the zone of direct light in the zero degree to forty-five degree zone by diagonal lines at 29, and the zone of downwardly emitted light near nadir intercepted by the lower lamp 25 by diagonal cross hatching at 30.

On the right of Figure 2, the zone of upwardly emitted light from the lower lamp 25 falling on the upper lamp 24 is indicated by cross hatching at 3B, the zone of reflected light by vertical lines at 3|, the zone or direct light beyond the r forty-five degree zone from nadir by horizontal lines at 32, and the zone of direct light by slanting lines at 33. This arrangement has approximately sixty per cent of the light in the zero to forty-five degree zone and fifteen per cent in the forty-five to ninety degree zone. It will thus be seen that the arrangement of two lamps in the axial plane of the symmetrical reflector has resultedin no practical loss of efliciency of light utilization over that obtained by the single lamp mounted in any typical way in the rear of the reflector. There has merely been a slight spreading out of the light so that more of it is in the forty-five to ninety degree zone. The fixture, however, may have all the lighting advantages of the two light installation but be of generally the dimension of the typical single lamp unit.

In the arrangement shown in Figure 3, lamps 24' and 25 of novel shape (and forming the subject matter of a separate application for Letters Patent, filed by the applicant on November 21, 1939, and serially numbered 305,440) are shown in place in the reflector 2|. These lamps are modified triangular cross-section with the apices toward the rear of the reflector. With this shape of lamp the amount of light lost toward zenith is very small and the amount of light lost by shadowing of one lamp by the other is also greatly reduced. With the arrangement, the overall efficiency of the unit may be slightly more than that of the typical single lamp unit, or the double lamp unit of Figure 2, and the light control may be such as to build up a higher efliciency in the zero to forty-five degree zone than could be obtained withthe same size reflector from the round lamp, with even less light in the forty-five to ninety degree zone than would be obtained from the single round lamp.

While the discussion given above relates to luminaires having symmetrical reflectors concaved toward the light sources, it is possible to obtain many of the advantages of the present invention in trough shaped reflectors of asymmetric profiles.

Where the output of light required is greater than the two lamps 24 and 25 will produce, it is possible to add an additional lamp below the first two. It will, of course, be understood that the showing of the drawing is more or less diagrammatic and that structural details are omitted.

Also, it is obvious that the invention may be embodied in other forms and constructions within the scope of the claims and I wish it to be understood that the particular forms shown are illustrative only. Various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.

What is claimed is:

l. A direct lighting luminaire comprising an elongated, open mouthed reflector which in transverse vertical section is a diverging open conic curve having a focus, linear fluorescent lamps mounted lengthwise within said reflector one above another and in substantially contacting relation, one of said lamps being disposed above the focal line and near the vertex of said reflector and the other lamp below the focal line of the reflector, with the line of substantial contact oi the lamps substantially coincidingwith the focal line of the reflector, the opaque light reflecting surface of each lamp intercepts light radiated by the other lamp throughout a substantial angle about the axis thereof and reflects said light laterally towards the sides of the reflector, the light raysfrom the lower lamp being projected by said reflector in a convergent beam and those from the upper lamp in a diwill be mixed and cover vergent beam so that the output of said lamps substantially the same area and any fluctuations of light intensity in the mixed output substantially eliminated.

2. A luminaire as in claim 1, wherein the lamps are of circular cross-section so that shadowing of one by the other is the same.

3. A luminaire as in claim 1, with the side walls of said lamps having downwardly and outwardly sloping upper surfaces tov reduce the interception of light from one lamp by the other.

4. A luminaire as in'claim 1, with the reflector similar on opposite sides of its axis and the lower of said lamps immediately back of the plane of the mouth of the reflector.

LEROY C. DOANE. 

